This invention relates to fuel compositions for internal combustion engines and more particularly to fuel compositions which are characterized as containing a lubricant. The compositions disclosed herein are especially suitable for operating two-cycle combustion engines.
It is an ongoing goal of the world's automotive industries to continuously develop more efficient combustion engines which at the same time release decreased levels of undesirable gaseous emissions during their operation. The most common type of combustion engine presently in popular usage is the four-cycle engine. During normal operation four strokes or motions of the piston and connecting rod assembly in the cylinder bore comprise one complete engine cycle. These strokes are: 1) fuel-air intake stroke, 2) compression stroke, 3) power stroke, and 4) exhaust stroke. This cycle is repeated over and over at a constant or varied rpm in order to provide a useful work output. One of the drawbacks of the four-cycle engine is that only one power stroke occurs during every two revolutions of the crankshaft to which the piston and its connecting rod are attached.
Two-cycle engines, on the other hand produce one power stroke for every one revolution of the crankshaft. Typical operation is as follows: On the upstroke of the piston a partial vacuum is created in the crankcase and the piston is simultaneously caused to uncover a fuel mixture inlet port forcing the fuel mixture to enter the crankcase. This occurs while the charge currently in the cylinder is being compressed. The compressed charge is then fired and the piston decends on its power stroke, compressing the mixture in the crankcase. At the bottom of the power stroke, the piston uncovers the exhaust port(s) and fuel transfer ports. The exhaust gasses exit the engine while fresh fuel mixture is admitted to the cylinder. The cycle then repeats.
For two cycle engines conventional fuel mixtures comprise a gasoline and a gasoline-soluble lubricating additive such as a petroleum oil in a ratio of about 16 parts gasoline to 1 part of lubricating additive. Several different lubricating additives are available under the name of "2-cycle engine oil". The main requirement of such an oil is to provide sufficient lubrication of the moving engine components so as to avoid engine seizure and undue wear while preventing build-up of carbon deposits in the combustion chamber. From a manufacturing standpoint, an advantage of using a fuel/lubricant mixture is that no oil flow passages must be cast in or machined in the engine block and that no oil recirculating system or pump is required. Therefore the cost of manufacturing two cycle engines is considerably less when compared to four-cycle engines. Also, since the engine delivers one power stroke per engine revolution using fewer moving parts, greater power is produced with relatively less cost and less pollution.
The major disadvantage of combusting fuel/lubricant mixtures and the main reason why these types of engines do not enjoy the same popularity as their four-stroke counterparts is that the amount of unburned hydrocarbons, carbon monoxide, or nitrogen oxides emmitted during their operation is too great for the current emmission standards maximum levels imposed by the US EPA and other similar organizations worldwide even when state-of-the-art catalytic convertors are utilized. Obviously if it were possible to reduce the quantity of undesirable emissions while maintaining sufficient lubrication for normal engine operation then the automotive industries and society as a whole would benefit greatly.